This invention relates to telecommunications networks and in particular a system and method for asynchronous transfer mode (ATM) transmission of traffic.
ATM technology is a flexible form of transmission which allows various types of service traffic, e.g. Voice, video or data, to be multiplexed together onto a common means of transmission, the traffic being carried in cells each having a header indicating its destination. Service traffic is adapted typically into 53 byte cells comprising 5 byte headers and 48 byte payloads such that the original traffic can be reconstituted at the far end of the ATM network. This form of adaption is performed in the ATM adaption layer (ML). The technique allows large volumes of traffic to be handled reliably and efficiently.
A limiting factor in the introduction of ATM is the difficulty of interfacing new broadband ATM networks with existing narrowband networks. The presently proposed AAL2 ATM trunking for narrowband services encapsulates and transports short user information packets inside an ATM cell stream. AAL2 allows multiple narrowband users to share a single ATM virtual circuitxe2x80x94in this manner the length of each user packet can be kept short to minimise packetisation delay, whilst the overall bandwidth efficiency of the VCC is maintained. However, as presently proposed, a single AAL2 virtual circuit can only support AAL2 connections which are controlled by the same type and variant of narrowband signalling system. In general, transmission facilities terminating on a single interworking function (IWF) may each carry a different narrowband signalling system, or a single transmission facility may carry multiple narrowband signalling systems. In either case, this requires the IWF to terminate and process multiple different narrowband signalling systems. This means that as presently proposed, in order to transport user data across the ATM network, the IWF would need to initiate multiple AAL2 virtual circuits, one for each narrowband signalling system terminated. At present it is not otherwise possible for the narrowband signalling handling function at the receiving IWF to determine which signalling system to associate with an individual narrowband call. This information is required so that the receiving IWF can successfully process the signalling information in order to provide onward routing of the call.
The use of multiple AAL2 virtual circuits to overcome this problem leads to an inefficient use of bandwidth, especially when an AAL2 virtual circuit has only a few calls to support.
It is an object of the present invention to minimise or to overcome these disadvantages.
It is a further object of the present invention to provide an improved apparatus and method for the transport of narrowband communications traffic over ATM networks.
In a first aspect the present invention provides a method of transporting narrowband calls of multiple narrowband signalling type between first and second narrow band networks across a virtual circuit in an ATM network, wherein for each call connection within said circuit the call connection signalling information includes the narrowband signalling type.
Preferably the call connection signalling information is a data packet comprising a narrowband signalling type field.
In a second aspect the present invention provides a method of transporting narrowband calls of multiple narrowband signalling type between first and second narrow band networks across an ATM network; the method comprising:
forming a virtual circuit;
forming call connections within said circuit with a call connection signalling information data packet comprising a narrowband signalling type field containing the narrowband signalling type of said call.
In a third aspect the present invention provides an apparatus for transporting narrowband calls of multiple narrowband signalling type between first and second narrow band networks across an ATM network, the apparatus comprising:
means for forming a virtual circuit;
means for forming call connections within said circuit by forwarding a call connection signalling information data packet comprising a narrowband signalling type field containing the narrowband signalling type of said call.
In a fourth aspect the present invention provides an apparatus for transporting narrowband calls of different signalling type between first and second narrow band networks across an ATM network, the apparatus comprising:
means for forming a virtual circuit;
means for forming call connections within said circuit by receiving a call connection data packet comprising a narrowband signalling system type field containing the narrowband signalling system type of said call.
Preferably said means is an interworking function.
Preferably said virtual circuit is an AAL2 virtual circuit.
In a further aspect the present invention provides a telecommunications system for transporting narrowband calls of different signalling type between first and second narrow band networks across an ATM network, the system comprising:
means for forming a virtual circuit between two interworking functions (IWF);
means for forming call connections within said circuit by transferring between said IWFs a call connection data packet comprising a narrowband signalling system type field containing the narrowband signalling system type of said call.